Dysplasia of the hip is a known illness, widespread throughout the world, which consists of an articular deformity that starts during the inter-uterine life of the baby but continues to evolve during the first years of life, which makes it an evolutionary illness.
Dysplasia manifests itself in an excessive looseness of the joint, which leads the femoral head to exit from and return inside the acetabular cavity when subjected to external forces. If this instability is not diagnosed and treated, as the months pass the femoral head, subjected to the action of the muscles and then the body weight, gradually loses its relation with its natural seating, or paleocotyl, and rises upward, configuring a permanent dislocation of the hip and defining a new seating, or neocotyl.
If diagnosed in newborns, dysplasia can be cured almost completely using spreaders, redefining the position of the joint.
If the dysplasia is not treated in time in the newborn, it can develop and reach an arthritic stage.
Depending on the stage reached, and provided that the articular function has been retained, it is possible to intervene using corrective surgical operations, such as re-orientation osteotomies, typically prosthetic surgery interventions. These procedures respectively have the purpose of improving the relation between the articular heads, preventing or retarding the onset of arthrosis, and of increasing the cover of the femoral head, thus slowing down the progression of the illness.
These procedures consist in the resection of the femur at two points, in order to remove a portion thereof, normally from 1 to 4 cm in length, with the purpose of returning the head of the femur into the paleocotyl. From this osteotomy two bone stumps are produced, which are subsequently joined together again.
It is known to proceed using a flat osteotomy, in which the femur is sectioned with flat cuts. The disadvantage of this procedure is that, reconstructing the femur by rejoining the stumps sectioned by said flat cuts, the femur does not resist in the best possible way to the torsional stresses, and this can lead to a fracture or pseudo-arthrosis.
To overcome the disadvantages of flat osteotomy, it is known to operate using other variant types of osteotomy, such as for example V-shaped (chevron or double-chevron osteotomy), oblique or Z-shaped, which allow torsional stability of the joint. In fact, a V-shaped, oblique or Z-shaped cut of the femur allows a recoupling of the stumps that is resistant to torsional stresses.
It is known, during V-shaped, oblique or Z-shaped osteotomies, to use devices for the resection of the femur, applied to the femur itself using pins and/or Kirschner wires, with the purpose of defining a clean cut and of measuring the quantity of femur to be cut with the greatest accuracy. One example is described in the patent application JP-A-2005000526.
Known devices for the resection of the femur generally have a main resection body, parallelepiped shaped, suitable to rest on the femur.
The main resection body is a single piece, which has a plurality of resection grooves, mating in shape with the cut to be made, V-shaped for example, which function as a guide template for the cutting operation.
The resection grooves are suitably distanced from each other along the development of the femur so that the correct and desired portion can be removed, using only different and distanced resection grooves.
One disadvantage of known devices for the resection of the femur is that the profile of the cut made on the bone stumps does not allow them to rotate with respect to each other, that is, it allows them to be rejoined only if the profiles are flat and parallel, which condition occurs by not rotating the stumps. In particular, if the femur has an axial development with a certain torsional deformation, the rejoining of the stumps is imprecise and not effective.
This disadvantage occurs since very often subjects affected by dysplasia generally have a very pronounced anteversion of the neck of the femur, which is manifested with a great torsional deformation. In healthy subjects, the line of the neck is oriented forward by about 8-13°, while in subjects affected by dysplasia this value can go as high as 30° for example.
During the surgical osteotomy operation for treating dysplasia, it is therefore also usual to restore the anatomic anteversion of the femur by reciprocal mobilization of the stumps, that is, by rotating them with respect to each other, in order to orient the femoral prosthesis with respect to the acetabular prosthesis in the best possible way.
It is therefore necessary to make the two stumps able to be coupled precisely in said reciprocally rotated position.
Document US 2011/0015636 A1 describes a resection guide for the joint of the humerus, which provides two degrees of freedom: rotation and translation, along the axis of articulation of the humerus. The purpose of the guide is substantially to make a seating in the joint of the humerus where a prosthesis can be positioned.
The resection guide described in US 2011/0015636 A1 therefore concerns a bone segment, that of the humerus, which is different from the bone segment of the femur. Moreover, the guide works along the axis of articulation of the humerus, which is substantially parallel to the transverse anatomical plane of the human body and orthogonal to the longitudinal axis of the femur, which is perpendicular to the transverse anatomical plane of the human body. The guide is therefore unsuitable and ineffective for a resection of the femur and in particular for a resection of the femur that allows to define the length of the femur to be removed and the angle between the stumps, and to couple them precisely so that it is possible to intervene effectively in order to restore, in particular, the anatomical anteversion.
There is therefore a need to perfect a device for the resection of the femur, usable in orthopedic surgery operations, in particular minimally invasive prosthetic surgery, which can overcome at least one of the disadvantages of the state of the art.
In particular, one purpose of the present invention is to obtain a device for the resection of the femur that can be used in all types of osteotomy interventions.
Another purpose of the present invention is to obtain a device for the resection of the femur that allows to define the length of the femur to be removed and the angle between the stumps, so that they can be coupled precisely and so that it is possible to intervene effectively in order to restore the anatomical anteversion.
Another purpose is to obtain a device for the resection of the femur that is easy to use.
Another purpose of the present invention is to obtain a device for the resection of the femur that works substantially along the longitudinal axis of the femur.
Another purpose of the present invention is to obtain a device that can be used effectively also in the correction of the abnormal angulation of the proximal femur.
The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.